1. Field of the Invention
The present Invention relates to an image reading equipment for digital copying machines, facsimile machines, or the like and more particularly to a data control system which, being used for an image reading equipment, develops the signals representing the image on the original sheet in terms of density signals, converting the analog signals obtained by reading, by means of its sensor, the amount of the light reflected from the original sheet into digital signals, and thereafter transforming the said digital signals into density signals.
2. Description of the Prior Art
Image reading equipments, such as digital copying machines and facsimile machines, read the original sheet by means of a CCD line sensor and converts the analog signals into digital signals, with which such equipments perform the storing in memory, processing, and editing of the said signals and perform such processes as the registration of the image signals on the copying paper. The CCD line sensor which is used for this process of reading the original sheet, is designed to read the amount of the light reflected from the original sheet on which light is shed from the light source, and, in order to use the light so read as the recording signal, it is necessary to convert the said light into signals representing the density of the toner. Moreover, the CCD line sensor is designed also to be capable of simultaneously reading a plural number of picture elements and scanning them to transforming them into serial signals, in which form the said CCD line sensor takes the image signals into the system, and, furthermore, when the CCD line sensor is employed for a color image reading equipment, it is provided with filters for R (red), G (green), and B (blue), as set in an arrangement in the stated order, for the purpose of obtaining the color decomposing signals. Therefore, the signals read out of the CCD line sensor in such a case will be serial signals in the sequence, RGBRGB . . . . . . .
In this regard, it would not serve the purpose of practical use, in view of the wafer size, the yield, the cost, and so forth, that uniform sensitivity should be formed, without any fall-off, as one chip on a single board in the CCD line sensor. For this reason, it is a system in common practice to set up a plural number of chips arranged in the main scanning direction, so that the individual sensors together read the image of one line as divided among them and to apply the signal processing of the divided signal in each of the individual channels.
For example, there is a system in which five chips with the processing capacity of 2928 picture elements arranged in a zigzag pattern in a CCD line sensor which is capable of reading an original sheet of the standard A3 size. In a color image reading device like this, the signals RGBRGB as read out of the CCD line sensor are separated into R, G, and B, respectively, and a process is performed further to synthesize the R, G, and B in the individual channels to develop serial signals on the R, G, and B, respectively.
However, the characteristics of the photoelectric conversion by the CCD line sensor are such that there occurs a difference in the level of signals between the individual channels and the individual picture elements as illustrated in FIG. 39 (a), where the reading signal level for the white reference board is represented as "the white color" while the signal level at the dark time output with no input of light is represented as "the black color". Hence, it is conveivable to match the average level of the individual channels. However, such an adjustment would cause the occurrence of differences in the grades of density due to the differences in the level in the marginal parts of the individual channels. Moreover, it is also conceivable to match the level in the marginal parts of the individual channels, but an adjustment like this, which would eliminate the differences in the grade of density in the marginal parts of the channels, would nevertheless liable to the appearance of streaks or uneven coloring in the supplementary scanning direction on copies in consequence of the inconsistency caused to appear in the individual picture elements or in the region in the principal scanning direction in consequence of the fluctuations in the density level because there would be differences in the output even in the reading of an original sheet in the same density.
Furthermore, as lower values than those of the output from the normal picture elements are output while an original sheet with higher density is being read, the level of the density signal will be lower in relative terms, with the result that black streaks will be visually recognized in the output image, and, conversely, when higher values are output while an original sheet with higher density is being read, white streaks will be visually recognized in the output image.
Thus, the CCD line sensor presents such problems in the original sheet reading signal as the deviations between the chips, the deviations among the picture elements in a chip, and the differences in terms of their characteristics. In addition, the distribution of the amount of light from the light source, the fluctuations in the amount of light, the deterioration accompanying the passage of time, and so forth also present problems.